The present invention generally relates to an electron-beam heating apparatus and a heating method thereof, and more particularly to an electron-beam heating apparatus and a heating method which is used for performing a heat treatment for a material, such as a semiconductor, by means of electron-beam heating.
Generally, annealing of a material for semiconductors, which annealing performed in various manufacturing processes or in various activating processes, is performed by heating of the material. The annealing of material includes activation annealing of an ion-implanted semiconductor material, reflowing for planation of an insulating layer, and sintering of metal circuits. The activating process includes activating of thin film electronic devices on an insulating substrate in liquid crystal TFT. Particularly, for annealing technology in manufacturing process of highly integrated electronic devices such as semiconductor devices or thin film device, it is required to heat a surface in a short time without affecting inside the substrate. Electron-beam heating is suitable for this requirement. In order to heat a material, there are some methods such as using an electron-beam, a laser beam or a lamp beam. The electron-beam method has an advantage of wide application as compared to other methods as this method can be applied to any material for surface heating.
Conventionally, the electron-beam heating apparatus disclosed in "Plasma Annealing for Ion Irradiated Semiconductor", Appl. Phys. Lett.39(8), Oct. 15, 1981, written by N. J. Ianno et al., is known. This apparatus is schematically shown in FIG. 1. A chamber 50 is maintained in low vacuum by introducing 50-100 torr of helium gas. In this condition, a voltage difference of 10-80 mA is applied between a cathode 51 and an anode 52 so as to generate a discharge in two separate regions. One of the two regions is a cathode dark space formed near the cathode 51. The other is a negative glow-discharge region formed on the side of the anode 52 opposite to the cathode 51. In a stable condition, electrons are emitted from the cathode 51 by bombardment of ions in gas-discharge. These electrons are effected by a high intensity electric field in the cathode dark space region and are accelerated in a direction toward the negative glow-discharge region. These electrons are formed in an electron-beam having a high energy. On the other hand, little electric field is formed in the negative glow-discharge region, and the glow discharge is maintained by the high energy electron-beam from the cathode dark space region. A length of the glow-discharge region is equal to a length of the region where the high energy electron-beam exists. The high energy electron-beam, incident on a material 53 after passing through the glow-discharge region as a glow electron beam, performs annealing of the material 53. It should be noted that in the apparatus shown in FIG. 1, a magnetic lens 54 is additionally provided so as to focus the electron-beam on the material 53.
The merit of the apparatus is in that an energy of the electron-beam, which corresponds to a depth of penetration of electron, can be independently controlled from the power of the beam (number of electrons therein) required for annealing. Namely, the energy of the glow electron-beam can be independently varied by varying the voltage applied between the cathode 51 and the anode 52, and the power of the electron-beam can be varied by varying the pressure inside the chamber 50. The power of the electron-beam is proportional to the current flowing to the cathode. This characteristic of the glow electron-beam is advantageous particularly when annealing a material that has a slight damage, for example a material whose surface is implanted with ions. The above mentioned slight damage of the material includes, for example, an island-like amorphous layer formed on a surface layer of the material. The island-like amorphous layer may be caused, for example, by a lattice defect formed during ion implantation to an Si wafer; this amorphous layer may grow to a continuous amorphous layer. A lattice defect can be easily corrected by means of a relatively low temperature. However, an island-like amorphous layer requires a relatively long time and a relatively high temperature to be corrected. Further, activation of the island-like amorphous layer takes a relatively longer time to be corrected than the continuous amorphous layer. The glow-discharge electron-beam heating can perform an annealing for the above mentioned slight damage in a short time by selectively heating a region of a surface of the material at a predetermined depth.
However, it was discovered by the applicant that the above mentioned glow-discharge region is adjacent to an arc-discharge region where an arc discharge is generated, and that the glow discharge shifts to an arc discharge when an increase or a concentration of electric current occurs on a part of or on an entire surface of the cathode 51. If the glow discharge shifts to the arc discharge, the cathode dark space region formed near the cathode 51 is reduced. Accordingly, the acceleration of the electron-beam is reduced, resulting in that the energy of the electron-beam is decreased to a level insufficient to perform an annealing. Therefore, there is generated a fluctuation of the heating characteristics, and thus a good and stable annealing is not obtained.